Process for culturing lactococcus bacteria

ABSTRACT

This invention relates to an improved process for culturing bacteria of the family Streptococcaceae (such as of the genus  lactococcus ), a medium for culturing the bacteria, and the obtained bacteria cells.

FIELD OF INVENTION

This invention relates to an improved process for culturing bacteria ofthe family Streptococcaceae, a medium for culturing the bacteria, andthe obtained bacteria cells.

BACKGROUND OF INVENTION

Bacteria of the family Streptococcaceae (which are lactic acid producingbacteria) have previously been propagated in different media, such asmedia containing yeast extract. US patent application 20050032196 [INRA,France] discloses the propagation of lactic acid bacteria of the genusLactococcus lactis (which belongs to the family Streptococcaceae) in thestandard laboratory medium M17 which contains peptone, lactose and yeastextract.

There is still a need for providing improved media for propagatinglactic acid bacteria of the family Streptococcaceae, which media canresult in a higher yield of cells, and of cells having an improvedviability, thereby reducing the cost of production.

SUMMARY OF INVENTION

The present inventors have found that when cells of the familyStreptococcaceae, especially of the genus Lactococcus, are culturedaerobically in a medium containing biomass (“single cell protein” or anautolysate) obtained from a methanotrophic/methylotrophic microorganismof the species Methylococcus capsulatus, it is possible to obtain asurprisingly fast growth rate of the cells, a surprisingly fastadaptation of the cells to the medium at the start of the culturing, anda surprisingly high concentration of cells as compared to theconcentration of cells obtained when a similar medium containing yeastextract is used.

In accordance with this finding, the above objective has been solved bythe present invention, which in its broadest scope provides a processfor culturing a bacterium of the family Streptococcaceae in a nutrientmedium, which comprises biomass, obtained from a methylotrophic and/ormethanotrophic microorganism.

WO 03/089625 A2 [Norferm Da, Norway] discloses a method for culturingLactobacillus plantarum and Lactobacillus acidophilus (both of thefamily Lactobacillaceae) in a medium containing biomass of Methylococcuscapsulatus NCIMB 11132, Ralstonia sp. NCIMB 13287, Aneurinibacillus sp.NCIMB 13288 and Brevibacterium agri NCIMB 13289 (biomass produced asdescribed in WO 01/60974). From the growth tests (example 6) it can beconcluded that replacement of yeast extract with the same amount of BP(biomass of methanotrophic bacteria) in the MRS standard medium does notresult in an improvement in the number of viable cells (table 7 and 8;comparing row 2 with row 5 in both tables). WO 03/089625 A2 is silentabout culturing bacteria of the family Streptococcaceae.

In contrast to the above findings for Lactobacillus, the presentinventors have surprisingly found that replacement of yeast extract withthe same amount of BP when culturing a strain of Lactococcus results inan surprising improvement, such as in growth rate, see example 1 andFIG. 1.

DETAILED DISCLOSURE

In a first aspect, the present invention pertains to a process forpreparing (or propagating) a bacterial culture, including a lactic acidbacteria (LAB) culture (such as a starter culture or a probioticculture), comprising culturing at least one strain of the familyStreptococcaceae (such as of the following genera: Leuconostoc,Enterococcus, and Lactococcus) in a nutrient medium which comprisesbiomass obtained from a methylotrophic and/or methanotrophicmicroorganism. In other words, the invention pertains to a process forculturing (or propagating) a strain of the family Streptococcaceae, saidprocess comprises culturing in a nutrient medium as defined above, and aprocess for culturing (or propagating) a bacterial strain of the familyStreptococcaceae, comprising inoculating the bacteria in a nutrientmedium as defined above. Especially, the invention pertains to a processfor increasing the growth rate, and/or improving the viability of theStreptococcaceae cells.

The nature of the biomass is not crucial, it can be in the form of cellmaterial, such as whole cells; a lysate of the microorganism, such as anautolysate, hydrolysate or homogenizate; an extract of themicroorganism, such as the water soluble fraction of the lysed cell; ora mixture of any of these. The cell material, lysate or extract mayoptionally be treated, e.g. hydrolyzed, dried and/or filtrated. Theadvantageous effect of the biomass is anticipated to be present even ifa small amount of the biomass is added to the nutrient medium, but it ispreferred that the biomass, especially the extract or lysate, is presentin an amount of 0.1 to 50 g/L nutrient medium, such as in an amount of1-40 g/L; 3-30 g/L; 2-10 g/L; 0.1-10 g/L; 1-5 g/L or 5-15 g/L.

In an interesting embodiment, the methylotrophic and/or methanotrophicmicroorganism has been cultured on a substrate comprising as the primarycarbon and/or energy source a compound which is partly (compared to acarbohydrate) or fully reduced (or which contains carbon in a loweroxidation state than in carbon dioxide), such as on a substrate that, asthe primary carbon and/or energy source, contains a compound having aratio C/C+O (no. of carbon atoms/{no. of carbon atoms+no. of oxygenatoms}) in the range 0.6-1.0, such as in the range 0.8-1.0 or in therange 0.9-1.0. The substrate can comprise a compound selected from: analkane, preferably a C1-C6 alkane, such as methane, ethane, propane orn-butane; an alkanol, preferably a C1-C6 alkanol, such as ethanol ormethanol; and an alkene, preferably a C2-C6 alkene, such ethylene,propylene, or 1-butylene. Conveniently, the methylotrophic and/ormethanotrophic microorganisms have been produced by fermentation on asubstrate containing a hydrocarbon fraction or containing an alkanecontaining gas, such as natural gas. It is anticipated that somemicroorganisms (not being classified as a methylotrophic and/ormethanotrophic) are able to utilize a compound as defined above as acarbon source. The biomass of such a microorganism (e.g. when culturedon a substrate as defined above) may be used in the process forpreparing a bacterial culture. Such a process is an embodiment of thepresent invention.

In a preferred embodiment of the process of the invention, themethylotrophic and/or methanotrophic microorganism is a Methylococcusspecies, including Methylococcus capsulatus (such as NCIMB 11132). Othermicroorganisms that might be used include: Methylomonas species, such asM. rubra, M. methanica, M. gracilis, M. albus, M. clara, M. agile;Methylococcus species, such as M. luteus, M. ucrainicus, M.thermophilus; Methylosinus species, such as M. sporium, M.trichosporium; Methylocystis species, such as M. fistulosa and M.parvus, Methylobacter species, such as M. whitterbury, M. lutes.

In addition to the biomass of the methylotrophic and/or methanotrophicmicroorganism, the nutrient medium may contain biomass (such as wholecells, an extract or a lysate) obtained from at least one of thefollowing species: Ralstonia sp. (inc. NCIMB 13287), Aneurinibacillussp. (inc. NCIMB 13288) and Brevibacterium sp., such as B. agri (inc.NCIMB 13289). It is presently preferred that the biomass is “BioProtein”(essentially spray-dried autolysed Methylococcus capsulatus) obtainablefrom Norferm AS, Norway. The biomass can be produced as disclosed in WO01/60974, but it is anticipated that also a fraction of theMethylococcus biomass can be used in the process of the invention. Sucha fraction may be a lysate wherein a component (e.g. a component whichhas an negative effect on the LAB or the yield of the process) has beenremoved.

The nutrient medium may comprise at least one further component, such asa carbohydrate (incl. lactose or glucose); and/or a complex component(such as yeast extract or a peptone); and/or a porphyrin source (such asblood or a fraction thereof, including heme and hemin); and/or a mineralsalt.

In a preferred embodiment, the strain of the family Streptococcaceaebelongs to a species selected from the group consisting of Lactococcussp. (such as Lactococcus lactis subsp. lactis (including biovardiacetylactis) or Lactococcus lactis subsp. cremoris); Leuconostoc sp.(including Leuconostoc mesenteroides); and Enterococcus sp.

The physical parameters of the process of the invention is notanticipated to be critical, but it is presently preferred that theculturing is carried out under aeration, e.g. the culture is aerated soas to maintain an oxygen content, which is at least 2 micromoles perliter of culture medium. The temperature is preferably in the range of20-45 degrees C., such as in the range of 25-40 or 30-35 degrees C.

The process of the invention may further comprise at least one stepsselected from: harvesting the bacteria, preferably between 5 and 24hours after the start of the culturing, such as by centrifugation orfiltration; storing the harvested bacteria, such as at approximately 1-5degrees C; freezing or lyophilizing the harvested bacteria; storing thefrozen or lyophilized bacteria; and packaging the harvested bacteria(optionally in frozen or lyophilized form).

In a second aspect, the invention pertains to a nutrient medium forpropagating bacteria (including LAB) of the family Streptococcaceae,which medium is defined as above, such as a medium which contains wholecells, an extract or a lysate of a Methylococcus species, includingMethylococcus capsulatus.

In a third aspect, the invention pertains to a process for preparing aLAB culture (including a starter culture) comprising culturing at leastone strain of the genus Lactococcus under aeration in a nutrient mediumof the invention.

In a fourth aspect, the invention pertains to a LAB culture (including astarter culture) obtained by the process of the invention, such as aculture of Lactococcus lactis, including Lactococcus lactis subspecieslactis and cremoris. The culture of the invention differs from the knowncultures of the same species in that its cellular components areoptimized for a high growth rate and a high viability, possible due tothe culture containing specific components originating from the growthmedium.

In a fifth aspect, the invention pertains to a method for preparing afermented product, comprising inoculating a medium (such as milk or acrop) to be fermented with a lactic acid bacteria starter cultureaccording to the invention. The prepared fermented product is also anaspect of the present invention.

In a further aspect, the invention pertains to the use of biomassobtained from a microorganism cultured on a substrate that, as theprimary carbon and/or energy source,

-   -   does not contain a carbohydrate; and/or    -   contains a compound having a ratio C/C+O (no. of carbon        atoms/{no. of carbon atoms+no. of oxygen atoms}) in the range        0.6-1.0, such as in the range 0.8-1.0 or in the range 0.9-1.0;        and/or    -   contains an alkane, preferably a C1-C6 alkane, such as methane,        ethane, propane or butane; and/or    -   contains an alkanol, preferably a C1-C6 alkanol, such as ethanol        or methanol; and/or    -   contains an alkene, preferably a C2-C6 alkene, such ethylene,        propylene, or 1-butylene;        for the preparation of a medium for preparing/propagating        bacteria (including LAB) of the family Streptococcaceae. In a        preferred embodiment, the invention relates to the use of the        biomass obtained from a Methylococcus species, including biomass        from autolysed Methylococcus capsulatus cultured on a substrate        as defined above, for the preparation of a medium for        preparing/propagating lactic acid bacteria of the family        Streptococcaceae, including the genus Lactococcus.

DEFINITIONS

In the present context the term “strain of the family Streptococcaceae”designates a bacterial strain of one of the following genera:Streptococcus, Leuconostoc, Oenococcus, Pediococcus, Aerococcus,Gemella, Enterococcus, and Lactococcus; all of which are facultativeanaerobic, catalase-negative, fermentative, G+cocci. Examples of speciesincluded within this term are: Enterococcus aerogenes, Enterococcusfaecium, Lactococcus (previously Streptococcus) lactis, Lactococcuslactis subsp. lactis, Lactococcus lactis subsp. lactis biovar.diacetylactis, Lactococcus lactis subsp. diacetylactis (previouslyStreptococcus diacetylactis), Lactococcus lactis subsp. cremoris,Lactococcus acidophilus, Lactococcus cremoris, Leuconostoc carnosum,Leuconostoc citrivorum, Leuconostoc dextranicum, Leuconostocmesenteroides subsp. cremoris, Leuconostoc pseudomesenteroides,Oenococcus oeni (previously Leuconostoc oenos), Pediococcusacidilactici, Pediococcus pentosaceus, Streptococcus salivarius subsp.thermophilus, Streptococcus cremoris, Streptococcus diacetylactis,Streptococcus durans, Streptococcus faecium, Streptococcus lactis andStreptococcus thermophilus (previously Streptococcus salivarius subsp.thermophilus).

The term “carbon source” refers to a material containing at least onecarbon atom which can be enzymatically converted into an intermediatefor subsequent conversion into the desired carbon end-product. Exemplarycarbon sources include biomass, starches, dextrins and carbohydrates.

The term “culture” is well known in the art, and includes a culturecontaining a single strain of a bacterium, or more than one bacterialstrain. The term “starter culture” is well known in the art, andincludes a bacterial culture that is suitable for use in e.g. dairiesand agriculture (silage). The term “probiotic culture” is well known inthe art and includes a culture of bacteria capable of passing thegastro-intestinal tract in an essentially viable and live form andoptionally also being capable of stimulating the host's immune system.

The term “methylotrophic microorganism” includes microorganisms that canuse, as substrates for growth, C1 compounds containing carbon in a loweroxidation state than in carbon dioxide (such as methanol, methylamine,and methane). The term “methanotrophic microorganism” includesmicroorganisms that can utilize the gas methane. Methanotrophicmicroorganisms are often considered to be a subset of methylotrophicmicroorganisms. Examples on methanotropic/methylothopic microorganismsare: Methylomonas species, such as M. rubra, M. methanica, M. gracilis,M. albus, Methylomonas 16a (US6689601B2), M. clara, M. agile;Methylococcus species, such as M. luteus, M. ucrainicus, M.thermophilus, M. capsulatus; Methylosinus species, such as M. sporium,M. trichosporium; Methylocystis species, such as M. fistulosa and M.parvus, Methylobacter species, such as M. whitterbury, M. lutes.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the invention (especially in the context of thefollowing claims) are to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. The terms “comprising”, “having”, “including” and “containing”are to be construed as open-ended terms (i.e., meaning “including, butnot limited to,”) unless otherwise noted. Recitation of ranges of valuesherein are merely intended to serve as a shorthand method of referringindividually to each separate value falling within the range, unlessotherwise indicated herein, and each separate value is incorporated intothe specification as if it were individually recited herein. All methodsdescribed herein can be performed in any suitable order unless otherwiseindicated herein or otherwise clearly contradicted by context. The useof any and all examples, or exemplary language (e.g., “such as”)provided herein, is intended merely to better illuminate the inventionand does not pose a limitation on the scope of the invention unlessotherwise claimed. No language in the specification should be construedas indicating any non-claimed element as essential to the practice ofthe invention. All references mentioned herein are hereby incorporatedby reference herein in their entireties.

EXAMPLES Example 1 Growth of Lactococcus in Media with Added Bioprotein

Lactococcus lactis strain CHCC2862 (obtainable from Chr. Hansen A/S,Denmark) was used to inoculate 1.5 L medium as specified below in a 2 LApplicon fermenter with pH and temperature control. The pH wascontrolled by addition of concentrated ammonia to 5.9. The temperaturewas constant at 34° C., and stirring was maintained at a high level at1200 rpm in order to ensure efficient aeration from a 0.5 vvm air flow.The medium used was the standard growth medium M17 with extra addedlactose (40 g/L) and Hemin (1 ppm) in order to enable extended growth(control medium).

Fermentations with the additions to the above medium as described in thefollowing table were performed. BioProtein (essentially consisting ofspray-dried autolysed Methylococcus capsulatus biomass) was obtainedfrom Norferm AS (Norway), yeast extract was obtained from BioSpringer(no. 0207), and Hemin was obtained from Fluka (prod. no. 51280).

Biomass measured as optical density (600 nm), hours after start Addition2 5 8 15(end) None (control) 0 2 8 20 Yeast extract (5 g/L) 0 3 15 23BioProtein (5 g/L) 2 11 22 23

Addition of BioProtein obviously is a large improvement. The improvementis significantly larger than the improvement obtained with addition ofyeast extract, especially early in the fermentation. Further advantagesof adding BioProtein are revealed from the growth curves (see FIG. 1),such as (i) the growth starts immediately, (ii) the growth rate is fast,(iii) the cells can be harvested early after the start of the culturing,and (iv) the final amount of biomass/number of viable cells is high.

In summary: The addition of Bioprotein is a very large improvement ofthe growth of Lactococcus lactis, both with respect to fermentation timeand biomass yield.

Example 2

Lactococcus lactis strain CHCC2862 was used to inoculate 1.5 L medium asspecified below in a 2 L Applicon fermenter with pH and temperaturecontrol. The pH was controlled by adding concentrated ammonia to 5.9.The temperature was constant at 34° C., and stirring was maintained at ahigh level at 1200 rpm in order to ensure efficient aeration from a 0.5vvm air flow. The medium used was the standard growth medium M17 withextra added lactose (40 g/L) (control medium). Yeast extract orBioprotein were added to the control medium as defined in the table.

Medium Lactococcus lactis M17 + 40 g/L lactose (control) Control +Biospringer yeast extract (5 g/L) + Control + BioProtein (5 g/L) ++ +:Growth somewhat better than the control ++: Growth significantly betterthan the control

Example 3

Using the same conditions as in example 2, Lactococcus cremoris strainCHCC4462 (obtainable from Chr. Hansen A/S, Denmark) is propagated in thefollowing media:

Medium Lactococcus cremoris M17 + 40 g/L lactose (control) Control +Biospringer yeast extract (5 g/L) + Control + BioProtein (5 g/L) ++ +:Growth somewhat better than the control ++: Growth significantly betterthan the control

Preferred embodiments of this invention are described herein, includingthe best mode known to the inventors for carrying out the invention.Variations of those preferred embodiments may become apparent to thoseof ordinary skill in the art upon reading the foregoing description. Theinventors expect skilled artisans to employ such variations asappropriate, and the inventors intend for the invention to be practicedotherwise than as specifically described herein. Accordingly, thisinvention includes all modifications and equivalents of the subjectmatter recited in the claims appended hereto as permitted by applicablelaw. Moreover, any combination of the above-described elements in allpossible variations thereof is encompassed by the invention unlessotherwise indicated herein or otherwise clearly contradicted by context.

REFERENCES

-   U.S. Pat. No. 6,689,601 B2-   US 2005/0032196 A1-   WO 03/089625 A2-   WO 01/060974 A2

All references cited in this patent document are hereby incorporatedherein in their entirety by reference.

The invention claimed is:
 1. A process for preparing a bacteria culture,comprising culturing a Lactococcus lactis strain under aeration in anutrient medium comprising a biomass of a methanotrophic Methylococcuscapsulatus bacterium, wherein the biomass is selected from the groupconsisting of a hydrolysate of the Methylococcus capsulatus bacterium, ahomogenate of the Methylococcus capsulatus bacterium, an autolysate ofthe Methylococcus capsulatus bacterium, and a water soluble extract ofthe Methylococcus capsulatus bacterium, and wherein the biomass ispresent in an amount of 5 to 40 g/l of the nutrient medium, therebypreparing a bacterial culture.
 2. The process of claim 1, wherein thehydrolysate, homogenate, autolysate, or water soluble extract optionallyis treated by hydrolysis, drying, filtration, or a combination thereof.3. The process of claim 1, wherein the Methylococcus capsulatusbacterium is produced by culturing the bacterium on a substratecomprising as the primary carbon and/or energy source a compound whichis partly or fully reduced.
 4. The process of claim 3, wherein thesubstrate as the primary carbon and/or energy source contains a compoundhaving a ratio of C/C+O in the range of 0.6-1.0.
 5. The process of claim1, wherein the Methylococcus capsulatus bacterium is produced byculturing the bacterium on a substrate comprising as the primary carbonsource a compound selected from the group consisting of an alkane, analkanol and an alkene.
 6. The process of claim 1, wherein theMethylococcus capsulatus bacterium is produced by fermentation on asubstrate containing a hydrocarbon fraction or containing an alkanecontaining gas.
 7. The process of claim 1, wherein the nutrient mediumfurther comprises biomass of a microorganism selected from at least oneof Ralstonia sp, Aneurinibacillus sp. and Brevibacterium.
 8. The processof claim 1, wherein the nutrient medium further comprises one or moreselected from the group consisting of an additional carbon source, ayeast extract, a mineral salt, or a combination thereof.
 9. The processof claim 1, wherein the Lactococcus lactis strain is selected from thegroup consisting of Lactococcus lactis subsp. lactis, Lactococcus lactissubsp. lactis biovar. diacetylactis, and Lactococcus lactis subsp.cremoris.
 10. The process of claim 1, further comprising maintaining theoxygen content of the culture at a level of at least 2 micromoles perliter of culture medium.
 11. The process of claim 1, further comprisingharvesting the prepared bacteria culture.
 12. The process of claim 4,wherein the alkane is a C1-C6 alkane selected from the group consistingof methane, ethane, propane and n-butane.
 13. The process of claim 4,wherein the alkanol is a C1-C6 alkanol selected from the groupconsisting of ethanol and methanol.
 14. The process of claim 4, whereinthe alkene is a C2-C6 alkene selected from the group consisting ofethylene, propylene, and 1-butylene.
 15. The process of claim 6, whereinthe alkane containing gas is natural gas.
 16. The process of claim 7,wherein the Ralstonia sp. strain is NCIMB 13287, the Aneurinibacillussp. strain is NCIMB 13288 and the Brevibacterium sp. strain is NCIMB13289.
 17. The process of claim 8, wherein the carbon source is acarbohydrate selected from the group consisting of lactose and glucose.18. The process of claim 11, wherein the bacteria culture is harvestedbetween 5 and 24 hours after the start of the culture.